Anesthesia is commonly induced in a patient by means of an inhaled gaseous mixture comprised of anesthetic agent vapor, oxygen and a balance gas such as nitrous oxide, nitrogen, or helium delivered by an anesthetic gas delivery apparatus. For adequate control of the administration of a drug to a patient, it is essential that, not only the drug, but also the carrier gas be positively and accurately identified to ensure that, amongst other things, the rate of flow of carrier gas can be accurately controlled.
It is known to provide the yoke on the anaesthetic delivery apparatus with formations specific to a particular gas which can mate with corresponding formations on a cylinder containing that gas. The formations and keying systems are covered by recognized industry standards known as ISO 407. The formations on the yoke and the cylinder commonly take the form of cooperating pins and corresponding sockets or recesses respectively. The formations can prevent an incorrect cylinder from being fitted to the yoke.
The use of a series of mating formations on the yoke and the cylinder to identify the gas contained within the cylinder has been found to provide the necessary ability to identify accurately the gas within the cylinder. However, in order for anaesthetic delivery apparatus to be capable of taking a range of gases from respective cylinders, it is necessary for the yokes on which the cylinders are mounted on the apparatus to have formations for mating with each different cylinder type. This can increase the space requirement of the yokes on the apparatus to an unacceptable level. Furthermore, it requires appropriate components to be provided, calibrated for each specific gas, to allow flow of a selected carrier gas from its respective yoke into the delivery apparatus for use.